#! /usr/bin/env python3.6

_set = set([1,2,3])

input = int(input('add a item: \n'))

if input in _set:
    _set.add(input)
    print('has some like item, didn\'t add a new item.', _set)
else:
    _set.add(input)
    print('add a new item. ', _set)